This invention relates to an elevator control system for controlling an elevator car in a digital manner to permit the car to be operated in the normal mode immediately after the end of an emergency such as an electric power failure.
It is well known that the control of elevator systems has been previously accomplished by operating the elevator car according to a miniature model including a small movable body representative of the elevator car and a small-sized replica of the shaft. That is, the elevator car has been operated under one kind of copy control relying on an analogue miniature model and the dimension of the model has been greatly restricted by both the technique of manufacturing it and the accuracy thereof. On the other hand, high buildings recently being built have encountered problems in the production and installation of miniature models because they become large-scaled. This has coincided with advances in the construction of electronic parts and has resulted in attempts to conduct the control of elevator systems by utilizing a logic operation on the basis of digital positional information.
In controlling elevator systems on the basis of the digital logic operation as above described, the detected positional signal indicates the actual position and the actual amount of movement of the associated elevator car. In elevator control systems, an emergency such as an electric power failure may occur which causes a decrease or loss of the control function. Under these circumstances, the emergency suspension is caused to stop the elevator car by the action of the mechanical brake for purposes of safety. However, it is impossible by the operation of the brake to instantaneously stop the associated hoist and elevator car due to their inertias. The car continues to be moved until the braking force overcomes these inertia forces whereupon the car is stopped. Under these circumstances, it is important to know the position of the car within the associated shaft where it has been stopped.
After the end of the particular emergency, conventional elevator control systems have been returned to the normal mode of operation as follows: Because the position of the stopped elevator car is not known, the car has been first moved in a predetermined direction at a predetermined speed according to the automatic operation until it is stopped at a predetermined floor by means of a signal derived from a special position sensor disposed within the associated shaft. Thereafter the car is put in the normal mode of operation. Alternatively, the elevator car has been able to be manually moved to that floor nearest to the position of the stopped car on the basis of the sense of sight until it is stopped at that floor. Then the car is operated in the normal mode. In elevator systems controlled with the digital positional signal without the use of the miniature model as above described, it is necessary to take either one of the abovementioned measures.